Field of the Invention
The present disclosure relates to a display device capable of performing a touch sensing, a method for driving the same, and a driving circuit of the display device.
Discussion of the Related Art
User interface (UI) is configured so that users are able to communicate with various electronic devices and thus can easily and comfortably control the electronic devices as they desire. Examples of the user interface include a keypad, a keyboard, a mouse, an on-screen display (OSD), and a remote controller having an infrared communication function or a radio frequency (RF) communication function. User interface technology has continuously expanded to increase user's sensibility and handling convenience. The user interface has been recently developed to include touch UI, voice recognition UI, 3D UI, etc.
The touch UI has been necessarily adopted to portable information appliances. The touch UI is implemented by forming a touch screen on the screen of a display device. The touch screen may be implemented as a capacitive touch screen. The touch screen having capacitive touch sensors senses changes (i.e., changes in charges of the touch sensor) in a capacitance resulting from an input of a touch driving signal when a user touches (or approaches) the touch sensor with his or her finger or a conductive material, and thus detects a touch input.
In order to increase touch sensitivity of the capacitive touch screen the user feels, it is necessary to increase a touch report rate. This is because coordinates of the touch input are updated using a frequency of the touch report rate in a host system. Thus, a response time of the host system in response to the touch input is proportional to the touch report rate.
In an in-cell touch sensor technology in which the touch sensors of the touch screen are embedded in a pixel array of a display panel, because one display frame period is time-divided into a display period and a touch period, it is difficult to improve the touch report rate. In the in-cell touch sensor technology, the touch report rate is generally set to be the same as a display frame rate. The touch report rate indicates a frequency at which coordinate data obtained by sensing all of the touch sensors included in the touch screen is transmitted to the external host system. The display frame rate indicates a frequency at which all of pixels of the display panel are updated to new data. As the touch report rate increases, a time required to update coordinates of the touch input is reduced. Therefore, the touch sensitivity of the touch screen the user feels can be improved, and a touch input trace can be represented in detail. However, because a related art recognizes the touch input at the touch report rate, which is set to be the same as the display frame rate, it is difficult to implement the fast response of the touch input. For example, in case of a fast moving line drawn by a finger, the slow response of the touch input may cause an increase in a distance between successively recognized coordinate points. Hence, the related art may recognize a line of a shape different from a representation of a curved line the user draws.
In order to increase the touch report rate in the in-cell touch sensor technology, as shown in FIG. 1, a method for assigning a plurality of touch frames TF1 and TF2 to one display frame period has been proposed. In FIG. 1, M01 to M14 denote multiplexers used to sequentially sense touch blocks of a touch screen. Each touch block includes a plurality of touch sensors. Each of the touch frames TF1 and TF2 includes a plurality of touch periods respectively corresponding to the multiplexers M01 to M14. One touch frame indicates a cycle, in which a touch report is output. The multiplexers M01 to M14 are sequentially turned on in the touch periods. The touch periods occur when the touch enable signal TEN has a low logic level. Hence, a sensing unit sequentially sense changes in capacitances of the touch sensors through the multiplexers M01 to M14 on a per block basis. During one touch frame TF, each of the multiplexers M01 to M14 is used to perform a sensing operation once. Therefore, as shown in FIG. 1, when the two touch frames TF1 and TF2 are assigned to one display frame period, each of the multiplexers M01 to M14 is used to perform sensing operations twice.
However, in the related art in-cell touch sensor technology, a surplus period TD unusable as the touch period is produced in one display frame period. Because a length of the surplus period TD is shorter than a length of one touch frame, the surplus period TD is not used as the touch period. A reason why the surplus period TD is produced is because the touch report rate, which is integer times higher than the display frame rate, was implemented in the related art in-cell touch sensor technology.
The surplus period TD is necessarily produced in each display frame period. Hence, the related art in-cell touch sensor technology had a limit to an increase in the touch report rate because of the surplus period TD.